The invention relates to hybrid vehicle powertrains, including an internal combustion engine and an electric motor, wherein driving torque of the engine is supplemented with motor torque.
It is possible to reduce power losses inherent in a powertrain for motor vehicles by supplementing driving torque developed by an internal combustion engine with electric motor torque. A hybrid vehicle driveline of this kind is described, for example, in copending U.S. patent application Ser. No. 09/353,290, filed Jul. 15, 1999, entitled xe2x80x9cTRANSMISSION AND CONTROL SYSTEM FOR USE WITH AN ENGINE IN A HYBRID ELECTRIC VEHICLE.xe2x80x9d The copending application is assigned to the assignee of the present invention.
The powertrain of the copending application combines the advantages of an internal combustion engine with the advantages of an electric motor drive, thereby improving fuel economy and reducing undesirable exhaust gas emissions from the internal combustion engine.
The internal combustion engine can be deactivated when the vehicle is at rest. The induction motor can be used to complement the engine torque to provide added launch performance. During vehicle coast-down, regenerative braking is achieved, thereby further improving fuel economy.
The electric motor of a hybrid powertrain replaces the hydrokinetic torque converter included in most contemporary multiple-ratio automatic transmissions for automotive vehicles. A torque converter provides added torque for acceleration, but it also functions as a fluid coupling to attenuate engine torque variations during acceleration as well as during steady-state operation. Because of the absence of a torque converter in a hybrid powertrain, there is a need to effect by other means the necessary driving torque management and attenuation of inertia forces in the powertrain.
The improved powertrain of the invention makes it possible to achieve driving torque management and inertia force control in a hybrid powertrain. It includes a power flow path developed by an electric motor (i.e., a starter motor/alternator unit) packaged in parallel disposition with respect to a conventional internal combustion engine. The parallel power flow path will allow the internal combustion engine to be disconnected from the driveline when the vehicle stops or coasts. When the vehicle operates under low-power driving conditions, the power flow path for the motor may be used exclusively.
Energy may be recovered during coasting with the vehicle in a coast-braking mode. During heavy throttle acceleration, the added torque available from the motor can augment the torque of the internal combustion engine.
The improved hybrid powertrain of the invention includes a motor/alternator unit with an integral wet clutch. A torsional spring damper is located on the torque output side of the engine and on the torque input side of the wet clutch. The torque output side of the wet clutch is connected to the rotor of the electric motor/alternator unit, which results in reduced clutch gain and improves engagement quality of the clutch during transitions into and out of the electric motor drive mode.
The torque input side of the damper is connected to the engine crankshaft. It replaces the usual engine drive plate and starter ring gear assembly.
The clutch comprises a clutch cylinder that supports the rotor of the electric motor. The motor rotor and the clutch cylinder are rotatably supported on a stationary housing bearing support. Since the stator of the motor and the rotor are both piloted on the same stationary bearing support, accurate control of an electric motor air gap between the motor stator and the motor rotor can be maintained.
When the clutch is released, the motor can provide power directly to the input shaft of the transmission. When the clutch is engaged, the internal combustion engine is connected to the transmission input shaft, thereby enabling the motor to act as a starter motor for the engine. Engine vibrations are isolated by the torsional spring damper.
The electric motor rotor functions as an engine flywheel, thereby smoothing driveline disturbances.
The clutch friction elements are lubricated and cooled by transmission oil provided by a dedicated lubrication line. That oil is used further to cool the electric motor, which surrounds the clutch.